1. Field of the Invention
This invention relates to solar heat absorbers or collectors and more particularly to improved solar heat collectors for the heating of fluids such as water.
2. Description of the Prior Art
The art of solar collectors is well known. Also, there are several publications relating to solar collectors including "Now You Can Buy Solar Heating Equipment For Your Home", Popular Science, March 1975, Vol. 206, No. 3, pp 74-77, 136, 138-140, 142; "Energy from the sun: three new developments", Popular Science May 1975, Vol. 206, No. 5, described hereinafter as the Tungstun spike method; and "Magic Box Lets Sun Shine In", Washington Star News, December 1974; described hereinafter as the Gaydos compound method.
For many years there have been many unresolved conflicts among those skilled in the art of solar heat collection. Infrared energy has been treated both as electromagnetic wave energy and as bursts of energy within certain photon levels of atoms. It is known that atoms absorb certain amounts of energy in differing rates and release energy at the same rate or at different rates. It is not, however, understood how or why this occurs either directly or physically. Many experiments have resulted in hundreds of facts relating to the atomic structures of various elements when excited by infrared energy and their ability to absorb and release this energy. With this increase of knowledge the newest solar heat technology is finding better ways of collecting, exchanging and utilizing solar heat.
Some of the prior art, illustrated in the Popular Science article above, relates to the flat rooftop solar heat collectors, which normally includes a blackened copper or aluminum sheet to which a number of hollow tubes are attached. The collector is covered by a plate of transparent plastic or glass. When exposed to sunlight, the black metal sheet absorbs the solar heat and transfers it to fluid passing through the hollow tubes. The warm air or water within the tubes is then circulated throughout the house for heating same or it may be used or stored in hot water insulated tanks. The transparent plate of the solar collector allows the infrared radiation of the sun to pass through and heat the metal sheet, but at the same time the plate traps the infrared radiation that is given off by the metal and the heat is removed therefrom by the liquid passing through the tubes.
A proper design of an absorber requires a material which absorbs heat fast and has the ability to release it in desired amounts when needed. The basic prior art design of flat box absorbers was based on the concept of absorbing and removing heat as fast as possible, because the aluminum or copper atom absorbs and conducts or radiates at approximately the same rate.
Copper has one of the best absorption and conduction qualities for solar heat collectors of any substance within practical economics, but the operational technique of fast pumping causes much of the energy gained from the sun to be lost and the energy required to pump at a fast rate to be wasted. Also, the problem of high heat losses at higher temperatures necessary for turbine electrical generation and/or air conditioning systems compounds such losses.
The prior art has attempted to overcome these solar heating problems in the following manner:
A. Gaydos compound method: by increasing the specific heat without substantial loss of the absorbing quality, Gaydos developed a mixture of substances with the consistency of tar to employ as a solar absorber. This material apparently retains the solar heat collected while a slower pumping rate of the water through the tubes embedded therein removes the heat absorbed by such material. This method has certain apparent shortcomings including the fact that the collector must function at lower temperatures and there is a decrease in the absorption capabilities.
B. Tungsten spike method: Apparently stores the heat at very high temperatures without substantial radition loses, but the cost of material and production costs would prevent any wide commercialization of this method.
A flatbox collector of the prior art with curving tubes in a dead air space provides less heat collected as the mean temperature of the water heated is increased.
Thus, the efficiency of absoprtion drops off as the mean temperature of the water increases. This is due to losses of radiation from the absorbing surface to the collector enclosure and to the surrounding air about the collector. Increasing insulation and adding double plates of glass on the collector generally increase efficiency at higher temperatures of operation of the prior art.
Higher mean temperature of heated water is mandatory for operation of air conditioning equipment, yet for maximum heat collected lower operational temperatures are necessary. The problem then is to overcome heat losses by two method: larger storage and/or more collector surface. Larger storage allows for larger heat collected and extremely fast pumping is necessary to keep the collector at maximum efficiency. Large areas of collection or a greater number of collectors are also necessary to absorb enough heat to permit the use thereof in air conditioning systems.
Availability of solar energy is known to be directly related to local climate. The general estimate of solar energy hitting a collector surface in full direct sunlight is approximately 350 BUT hr/ft.sup.2. An efficiency rating for solar equipment must take into account not only the heat collected but how much energy was required to obtain the energy, electrical pumps, fans, etc. Efficiency of the heat collected must then be considered in view of total energy necessary to operate the solar energy collection system.
The patents to Wheeler U.S. Pat. No. 1,873,854 and 1,971,242 disclose solar collector systems in which water in a storage tank is recirculated back through additional tubing in the collector and heat is transferred from the hot coil to the recirculating coil so that the collector continues to heat and store water regardless of whether the water is being used. The invention disclosed herein is directed to a collector in which hotter fluid is recirculated within the collector, prior to leaving the collector whereby some of the heat is fed back from the hotter tube into the cooler tube and the fluid passing therethrough, and this increases the amount of heat or temperature of the water being discharged from the collector.
It is believed that energy carried along wavelengths can best be absorbed in phase relationship. The heat of the fluid in the hotter tube section may be transmitted to and absorbed by the fluid in the cooler tube section when the infra red energy being received by the cooler tube section is at a minimum at that location. Thus, this invention is based on the concept that heat is fed back from the hotter tube section into a cell or chamber which contains a cooler tube section and some of the heat from the hotter tube section is transferred into the cooler tube section and provides an ultimate hotter output from the collector. The collector herein disclosed employes tubing located and passing through a plurality of cells or dead air spaces to provide hotter and cooler tube sections for conducting both a hotter fluid and a cooler fluid respectively therethrough whereby heat is recirculated or transferred from the hotter tube section into the cooler tube section prior to leaving the collector.